Method of preparing a pharmaceutical cream and minimizing imiquimod impurity formation (at least six months storage)

ABSTRACT

Pharmaceutical formulations and methods including an immune response modifier (IRM) compound and an oleic acid component are provided where stability is improved by using oleic acid have low polar impurities such as peroxides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser. No. 12/334,255, filed Dec. 12, 2008 (now allowed), which application is a continuation of U.S. application Ser. No. 11/276,324, filed Feb. 24, 2006, which application is a continuation of U.S. application Ser. No. 11/303,659, filed Dec. 16, 2005, which application claims the benefit of U.S. Provisional Application Ser. No. 60/636,916 filed Dec. 17, 2004, the teachings of all being incorporated herein by reference in their entirety. This application also is a continuation of co-pending U.S. application Ser. No. 11/276,324, filed Feb. 24, 2006, which application is a continuation of U.S. application Ser. No. 11/303,659, filed Dec. 16, 2005, which application claims the benefit of U.S. Provisional Application Ser. No. 60/636,916 filed Dec. 17, 2004, the teachings of all being incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to pharmaceutical formulations for the topical or transdermal delivery of immunomodifying drugs.

BACKGROUND

There has been a major effort in recent years, with significant success, to discover new drug compounds that act by stimulating certain key aspects of the immune system, as well as by suppressing certain other aspects. These compounds, referred to herein as immune response modifiers (IRMs), appear to act through immune system mechanisms known as toll-like receptors to induce selected cytokine biosynthesis. They may be useful for treating a wide variety of diseases and conditions. For example, certain IRMs may be useful for treating viral diseases (e.g., human papilloma virus, hepatitis, herpes), neoplasias (e.g., basal cell carcinoma, squamous cell carcinoma, actinic keratosis, melanoma), and TH2-mediated diseases (e.g., asthma, allergic rhinitis, atopic dermatitis), and are also useful as vaccine adjuvants.

Many of the IRM compounds are small organic molecule imidazoquinoline amine derivatives (see, e.g., U.S. Pat. No. 4,689,338), but a number of other compound classes are known as well (see, e.g., U.S. Pat. Nos. 5,446,153, 6,194,425, and 6,110,929) and more are still being discovered.

One of these IRM compounds, known as imiquimod, has been commercialized in a topical formulation, ALDARA, for the treatment of actinic keratosis, basal cell carcinoma, or anogenital warts associated with human papillomavirus.

Pharmaceutical formulations containing IRM compounds are disclosed in U.S. Pat. Nos. 5,238,944; 5,939,090; and 6,425,776; European Patent 0 394 026; and U.S. Patent Publication 2003/0199538.

Although some of the beneficial effects of IRMs are known, the ability to provide therapeutic benefit via topical application of an IRM compound for treatment of a particular condition at a particular location may be hindered by a variety of factors. These factors include: irritation of the skin to which the formulation is applied; formulation wash away; insolubility of the IRM compound in the formulation; chemical degradation of the IRM compound and/or other ingredients, physical instability of the formulation (e.g., separation of components, thickening, precipitation/agglomerization of active ingredient, and the like); poor permeation; and undesired systemic delivery of topical IRM formulations if not intended to be transdermal.

Accordingly, there is a continuing need for new and/or improved IRM formulations.

SUMMARY

It has now been found that, while oleic acid can be used to solublize IRMs, even difficult to formulate, highly insoluble IRMs, formulations comprising an IRM compound in combination with oleic acid can suffer from impaired stability. Somewhat surprisingly, addition of greater amounts of antioxidants to the formulation does not solve the problem. However, it has been found that utilizing an oleic acid component having reduced amounts of polar impurities, such as peroxides, aldehydes, alcohols, and ketones in a formulation containing an IRM can reduce the formation of impurities and thereby provide improved formulation stability. Instability is an important issue for pharmaceutical formulations and can reduce the shelf life of a product or jeopardize regulatory approvability.

It has been discovered that the stability of a formulation containing an IRM compound and oleic acid can be improved by utilizing an oleic acid component that is free of or contains low amounts of polar impurities, such as peroxides, aldehydes, alcohols, and ketones. Although not intending to be bound to any particular theory or mechanism, it is hypothesized that the higher amounts of polar impurities present in the oleic acid component can react with the IRM compound, thereby destabilizing the formulation and increasing the rate of formation of impurities derived from the IRM compound.

In one aspect, the present invention provides a pharmaceutical formulation comprising a therapeutically effective amount of an immune response modifier (IRM) compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the formulation is substantially free of polar impurities introduced by the oleic acid component.

In another aspect, the present invention provides a pharmaceutical formulation comprising: a therapeutically effective amount of an IRM compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component has a peroxide value no greater than 5.

In another aspect, the present invention provides a pharmaceutical formulation comprising: a therapeutically effective amount of an IRM compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component is at least 80% oleic acid.

The present invention also provides methods.

In one aspect, the present invention provides a method of stabilizing a pharmaceutical formulation comprising a therapeutically effective amount of an immune response modifier (IRM) compound and oleic acid by using an oleic acid component that is substantially free of polar impurities.

In one aspect, the present invention provides a method of stabilizing a pharmaceutical formulation comprising a therapeutically effective amount of an IRM compound and oleic acid by using an oleic acid component with a peroxide value no greater than 5.

In one aspect, the present invention provides a method of stabilizing a pharmaceutical formulation comprising a therapeutically effective amount of an IRM compound and oleic acid by using an oleic acid component that is at least 80% oleic acid.

In another aspect, the present invention provides methods for treating disease, including but not limited to the group comprising actinic keratosis, basal cell carcinoma, genital warts, peri-anal warts, malignant melanoma, and molloscum contagiosum. In another aspect, the present invention provides methods to induce cytokine biosynthesis. In another aspect, the present invention provides methods to induce interferon biosynthesis.

A number of additional embodiments can be described as follows:

-   1. A pharmaceutical formulation comprising:

a therapeutically effective amount of an immune response modifier (IRM) compound selected from the group consisting of imidazoquinoline amines, tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine amines, oxazoloquinoline amines, thiazoloquinoline amines, oxazolopyridine amines, thiazolopyridine amines, oxazolonaphthyridine amines, thiazolonaphthyridine amines, 1H-imidazo dimers fused to pyridine amines, quinoline amines, tetrahydroquinoline amines, naphthyridine amines, or tetrahydronaphthyridine amines, and combinations thereof; and

a pharmaceutically acceptable vehicle including an oleic acid component, wherein the formulation is substantially free of polar impurities introduced by the oleic acid component.

-   2. A pharmaceutical formulation comprising:

a therapeutically effective amount of an IRM compound selected from the group consisting of imidazoquinoline amines, tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine amines, oxazoloquinoline amines, thiazoloquinoline amines, oxazolopyridine amines, thiazolopyridine amines, oxazolonaphthyridine amines, thiazolonaphthyridine amines, 1H-imidazo dimers fused to pyridine amines, quinoline amines, tetrahydroquinoline amines, naphthyridine amines, or tetrahydronaphthyridine amines, and combinations thereof; and

a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component has a peroxide value no greater than 5.

-   3. A pharmaceutical formulation comprising:

a therapeutically effective amount of an IRM compound selected from the group consisting of imidazoquinoline amines, tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine amines, oxazoloquinoline amines, thiazoloquinoline amines, oxazolopyridine amines, thiazolopyridine amines, oxazolonaphthyridine amines, thiazolonaphthyridine amines, 1H-imidazo dimers fused to pyridine amines, quinoline amines, tetrahydroquinoline amines, naphthyridine amines, or tetrahydronaphthyridine amines, and combinations thereof; and

a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component is at least 80% oleic acid.

-   4. A formulation as in any one of the preceding embodiments wherein     the IRM compound is selected from the group consisting of amide     substituted imidazoquinoline amines, sulfonamide substituted     imidazoquinoline amines, urea substituted imidazoquinoline amines,     aryl ether substituted imidazoquinoline amines, heterocyclic ether     substituted imidazoquinoline amines, amido ether substituted     imidazoquinoline amines, sulfonamido ether substituted     imidazoquinoline amines, urea substituted imidazoquinoline ethers,     thioether substituted imidazoquinoline amines, 6-, 7-, 8-, or     9-aryl, heteroaryl, aryloxy or arylalkyleneoxy substituted     imidazoquinoline amines, imidazoquinoline diamines, amide     substituted tetrahydroimidazoquinoline amines, sulfonamide     substituted tetrahydroimidazoquinoline amines, urea substituted     tetrahydroimidazoquinoline amines, aryl ether substituted     tetrahydroimidazoquinoline amines, heterocyclic ether substituted     tetrahydroimidazoquinoline amines, amido ether substituted     tetrahydroimidazoquinoline amines, sulfonamido ether substituted     tetrahydroimidazoquinoline amines, urea substituted     tetrahydroimidazoquinoline ethers, thioether substituted     tetrahydroimidazoquinoline amines, tetrahydroimidazoquinoline     diamines, amide substituted imidazopyridine amines, sulfonamide     substituted imidazopyridine amines, urea substituted imidazopyridine     amines, aryl ether substituted imidazopyridine amines, heterocyclic     ether substituted imidazopyridine amines, amido ether substituted     imidazopyridine amines, sulfonamido ether substituted     imidazopyridine amines, urea substituted imidazopyridine ethers,     thioether substituted imidazopyridine amines, and combinations     thereof. -   5. A formulation as in any one of embodiments 1 through 3 wherein     the IRM compound is an imidazonaphthyridine amine. -   6. A formulation as in any one of embodiments 1 through 3 and 5     wherein the IRM compound is     2-methyl-1-(2-methylpropyl)-1H-imidazo[4,5-c][1,5]naphthyridin-4-amine. -   7. A formulation as in any one of embodiments 1 through 3 wherein     the IRM compound is     1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine. -   8. A formulation as in any one of the preceding embodiments wherein     the IRM compound is present in an amount of at least 3% by weight,     based on the total weight of the formulation. -   9. A formulation as in any one of the preceding embodiments wherein     the IRM compound is present in an amount of at least 5% by weight,     based on the total weight of the formulation. -   10. A formulation as in any one of the preceding embodiments wherein     the oleic acid component is present in an amount of at least 15% by     weight based on the total weight of the formulation. -   11. A formulation as in any one of the preceding embodiments wherein     the oleic acid component is present in an amount of at least 20% by     weight based on the total weight of the formulation. -   12. A formulation as in any one of the preceding embodiments wherein     the oleic acid component is present in an amount of at least 25% by     weight based on the total weight of the formulation. -   13. A formulation as in any one of the preceding embodiments wherein     the oleic acid component has been purified by chromatography prior     to use in the formulation. -   14. A formulation as in any one of the preceding embodiments wherein     the oleic acid component is plant-derived. -   15. A formulation as in any one of the preceding embodiments wherein     the formulation includes at least one fatty acid other than oleic     acid or isostearic acid. -   16. A formulation as in any one of the preceding embodiments wherein     the formulation includes less than 3% isostearic acid by weight     based on the total weight of the formulation. -   17. A formulation as in any one of the preceding embodiments wherein     the formulation further comprises an antioxidant. -   18. A formulation as in any one of the preceding embodiments further     comprising an antioxidant, wherein the antioxidant is butylated     hydroxyl toluene or butylated hydroxyanisole. -   19. A formulation of any one of the preceding embodiments further     comprising water. -   20. A formulation of any one of the preceding embodiments further     comprising a preservative system. -   21. A formulation of any one of the preceding embodiments further     comprising an emulsifier. -   22. A method of stabilizing a pharmaceutical formulation comprising     a therapeutically effective amount of an immune response modifier     (IRM) compound selected from the group consisting of     imidazoquinoline amines, tetrahydroimidazoquinoline amines,     imidazopyridine amines, 6,7-fused cycloalkylimidazopyridine amines,     1,2-bridged imidazoquinoline amines, imidazonaphthyridine amines,     tetrahydroimidazonaphthyridine amines, oxazoloquinoline amines,     thiazoloquinoline amines, oxazolopyridine amines, thiazolopyridine     amines, oxazolonaphthyridine amines, thiazolonaphthyridine amines,     1H-imidazo dimers fused to pyridine amines, quinoline amines,     tetrahydroquinoline amines, naphthyridine amines, or     tetrahydronaphthyridine amines, and combinations thereof; and oleic     acid by using an oleic acid component that is substantially free of     polar impurities. -   23. A method of stabilizing a pharmaceutical formulation comprising     a therapeutically effective amount of an IRM compound selected from     the group consisting of imidazoquinoline amines,     tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused     cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline     amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine     amines, oxazoloquinoline amines, thiazoloquinoline amines,     oxazolopyridine amines, thiazolopyridine amines,     oxazolonaphthyridine amines, thiazolonaphthyridine amines,     1H-imidazo dimers fused to pyridine amines, quinoline amines,     tetrahydroquinoline amines, naphthyridine amines, or     tetrahydronaphthyridine amines, and combinations thereof; and oleic     acid by using an oleic acid component with a peroxide value no     greater than 5. -   24. A method of stabilizing a pharmaceutical formulation comprising     a therapeutically effective amount of an IRM compound selected from     the group consisting of imidazoquinoline amines,     tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused     cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline     amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine     amines, oxazoloquinoline amines, thiazoloquinoline amines,     oxazolopyridine amines, thiazolopyridine amines,     oxazolonaphthyridine amines, thiazolonaphthyridine amines,     1H-imidazo dimers fused to pyridine amines, quinoline amines,     tetrahydroquinoline amines, naphthyridine amines, or     tetrahydronaphthyridine amines, and combinations thereof; and oleic     acid by using an oleic acid component that is at least 80% oleic     acid. -   25. The method as in any one of embodiments 22 through 24 wherein     the IRM compound is selected from the group consisting of: amide     substituted imidazoquinoline amines, sulfonamide substituted     imidazoquinoline amines, urea substituted imidazoquinoline amines,     aryl ether substituted imidazoquinoline amines, heterocyclic ether     substituted imidazoquinoline amines, amido ether substituted     imidazoquinoline amines, sulfonamido ether substituted     imidazoquinoline amines, urea substituted imidazoquinoline ethers,     thioether substituted imidazoquinoline amines, 6-, 7-, 8-, or     9-aryl, heteroaryl, aryloxy, or arylalkyleneoxy substituted     imidazoquinoline amines, imidazoquinoline diamines, amide     substituted tetrahydroimidazoquinoline amines, sulfonamide     substituted tetrahydroimidazoquinoline amines, urea substituted     tetrahydroimidazoquinoline amines, aryl ether substituted     tetrahydroimidazoquinoline amines, heterocyclic ether substituted     tetrahydroimidazoquinoline amines, amido ether substituted     tetrahydroimidazoquinoline amines, sulfonamido ether substituted     tetrahydroimidazoquinoline amines, urea substituted     tetrahydroimidazoquinoline ethers, thioether substituted     tetrahydroimidazoquinoline amines, tetrahydroimidazoquinoline     diamines, amide substituted imidazopyridine amines, sulfonamide     substituted imidazopyridine amines, urea substituted imidazopyridine     amines, aryl ether substituted imidazopyridine amines, heterocyclic     ether substituted imidazopyridine amines, amido ether substituted     imidazopyridine amines, sulfonamido ether substituted     imidazopyridine amines, urea substituted imidazopyridine ethers,     thioether substituted imidazopyridine amines, and combinations     thereof. -   26. The method as in any one of embodiments 22 through 24 wherein     the IRM compound is an imidazonaphthyridine amine. -   27. The method as in any one of embodiments 22 through 24 and 26     wherein the IRM compound is     2-methyl-1-(2-methylpropyl)-1H-imidazo[4,5-c][1,5]naphthyridin-4-amine. -   28. The method as in any one of embodiments 22 through 24 wherein     the IRM compound is     1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine. -   29. A method of treating actinic keratosis, the method comprising     applying a formulation of any one of embodiments 1 through 21 to the     skin of a subject. -   30. A method of treating basal cell carcinoma, the method comprising     applying a formulation of any one of embodiments 1 through 21 to the     skin of a subject. -   31. A method of treating genital warts, the method comprising     applying a formulation of any one of embodiments 1 through 21 to the     skin or mucosal surface of a subject. -   32. A method of treating peri-anal warts, the method comprising     applying a formulation of any one of embodiments 1 through 21 to the     skin or mucosal surface of a subject. -   33. A method of treating molloscum contagiosum, the method     comprising applying a formulation of any one of embodiments 1     through 21 to the skin of a subject. -   34. A method of inducing cytokine biosynthesis, the method     comprising applying a formulation of any one of embodiments 1     through 21 to the skin or mucosal surface of a subject. -   35. A method of inducing interferon biosynthesis, the method     comprising applying a formulation of any one of embodiments 1     through 21 to the skin or mucosal surface of a subject.     A method of treating malignant melanoma, the method comprising     applying a formulation of any one of the preceding embodiments 1     through 21 to the skin of a subject.

The term “substantially free” is used to indicate that the amount present in the composition or formulation is below the level that causes degradation of the active pharmaceutical agent, such that the formulation is unsuitable for pharmaceutical usage, after storage for 4 months at 40° C. at 75% relative humidity. The term can also be used to describe a composition containing less than 10%, less than 5%, less than 1%, or less than 0.1% by weight of a given substance.

The term “polar impurities” includes, but is not limited to peroxides, aldehydes, ketones, alcohols, metal ions, and/or substances that cause degradation of the active pharmaceutical agent.

The term “oleic acid component” is used to describe a preformulation source or composition of matter containing oleic acid, and may include other fatty acids in addition to oleic acid, including but not limited to: myristic acid, palmitic acid, palmitoleic acid, margaric acid, isostearic acid, stearic acid, linoleic acid, linolenic acid, and other fatty acids, or combinations thereof.

The peroxide value is the number that expresses in milliequivalents of active oxygen the quantity of peroxide contained in 1000 g of the substance as determined by the methods described in the 5th edition of the European Pharmacopoeia, Section 2.5.5.

Unless otherwise indicated, all numbers expressing quantities, ratios, and numerical properties of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”.

All parts, percentages, ratios, etc. herein are by weight unless indicated otherwise.

As used herein, “a” or “an” or “the” are used interchangeably with “at least one” to mean “one or more” of the listed element.

The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

DETAILED DESCRIPTION

The present invention provides pharmaceutical formulations that include a therapeutically effective amount of an immune response modifier (IRM) compound selected from the group consisting of imidazoquinoline amines, tetrahydroimidazoquinoline amines, imidazopyridine amines, 6,7-fused cycloalkylimidazopyridine amines, 1,2-bridged imidazoquinoline amines, imidazonaphthyridine amines, tetrahydroimidazonaphthyridine amines, oxazoloquinoline amines, thiazoloquinoline amines, oxazolopyridine amines, thiazolopyridine amines, oxazolonaphthyridine amines, thiazolonaphthyridine amines, and 1H-imidazo dimers fused to pyridine amines, quinoline amines, tetrahydroquinoline amines, naphthyridine amines, or tetrahydronaphthyridine amines, and oleic acid, wherein the oleic acid component contains a low amount of polar impurities, especially peroxides. Surprisingly, the stability of such formulations is substantially greater than that of similar formulations containing an IRM compound and oleic acid containing conventional oleic acid with higher amounts of polar impurities such as peroxides, even when the oleic acid component is of compendial grade. Furthermore, the instability problem of these formulations is not eliminated by additional antioxidants.

Through utilization of an oleic acid component containing a very low amount of polar impurities, the subsequent formation of impurities in IRM formulations is significantly reduced as compared to other IRM formulations comprising compendial grades of oleic acid after both the initial measurement (i.e., its measurement when initially formulated) and under accelerated conditions (when stored for at least 4 months at 40° C. and 75% relative humidity), resulting in an increased formulation shelf life.

For certain embodiments, the formulation comprises an IRM compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the formulation is substantially free of polar impurities introduced by the oleic acid component. For certain embodiments, the formulation comprises an IRM compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component has a peroxide value no greater than 5. For certain embodiments, the formulation comprises an IRM compound and a pharmaceutically acceptable vehicle including an oleic acid component, wherein the oleic acid component is at least 80% oleic acid.

In certain embodiments, formulations described herein can be in the form of an oil-in-water emulsion such as a cream or a lotion. The oil component of the formulation includes an IRM compound and one or more fatty acids, including oleic acid in an amount sufficient to solubilize the IRM compound. Optionally, a cream or lotion of the invention can contain emollients, antioxidants, emulsifiers, viscosity enhancing agents, and/or preservatives. Such components, as well as all others of the formulations described herein, are preferably pharmaceutically acceptable.

Immune Response Modifying Compounds

Formulations of the invention include an IRM compound. Such compounds include, for example, imidazoquinoline amines including, but not limited to, substituted imidazoquinoline amines such as, for example, amide substituted imidazoquinoline amines, sulfonamide substituted imidazoquinoline amines, urea substituted imidazoquinoline amines, aryl ether substituted imidazoquinoline amines, heterocyclic ether substituted imidazoquinoline amines, amido ether substituted imidazoquinoline amines, sulfonamido ether substituted imidazoquinoline amines, urea substituted imidazoquinoline ethers, thioether substituted imidazoquinoline amines, 6-, 7-, 8-, or 9-aryl, heteroaryl, aryloxy or arylalkyleneoxy substituted imidazoquinoline amines, and imidazoquinoline diamines; tetrahydroimidazoquinoline amines including, but not limited to, amide substituted tetrahydroimidazoquinoline amines, sulfonamide substituted tetrahydroimidazoquinoline amines, urea substituted tetrahydroimidazoquinoline amines, aryl ether substituted tetrahydroimidazoquinoline amines, heterocyclic ether substituted tetrahydroimidazoquinoline amines, amido ether substituted tetrahydroimidazoquinoline amines, sulfonamido ether substituted tetrahydroimidazoquinoline amines, urea substituted tetrahydroimidazoquinoline ethers, thioether substituted tetrahydroimidazoquinoline amines, and tetrahydroquinoline diamines; imidazopyridine amines including, but not limited to, amide substituted imidazopyridine amines, sulfonamide substituted imidazopyridine amines, urea substituted imidazopyridine amines, aryl ether substituted imidazopyridine amines, heterocyclic ether substituted imidazopyridine amines, amido ether substituted imidazopyridine amines, sulfonamido ether substituted imidazopyridine amines, urea substituted imidazopyridine ethers, and thioether substituted imidazopyridine amines; 1,2-bridged imidazoquinoline amines; 6,7-fused cycloalkylimidazopyridine amines; imidazonaphthyridine amines; tetrahydroimidazonaphthyridine amines; oxazoloquinoline amines; thiazoloquinoline amines; oxazolopyridine amines; thiazolopyridine amines; oxazolonaphthyridine amines; thiazolonaphthyridine amines; and 1H-imidazo dimers fused to pyridine amines, quinoline amines, tetrahydroquinoline amines, naphthyridine amines, or tetrahydronaphthyridine amines.

These immune response modifier compounds are disclosed in, e.g., U.S. Pat. Nos. 4,689,338; 4,929,624; 5,266,575; 5,268,376; 5,346,905; 5,352,784; 5,389,640; 5,446,153; 5,482,936; 5,756,747; 6,110,929; 6,194,425; 6,331,539; 6,376,669; 6,451,810; 6,525,064; 6,541,485; 6,545,016; 6,545,017; 6,573,273; 6,656,938; 6,660,735; 6,660,747; 6,664,260; 6,664,264; 6,664,265; 6,667,312; 6,670,372; 6,677,347; 6,677,348; 6,677,349; 6,683,088; 6,756,382; U.S. Patent Publication Nos. 2004/0091491; 2004/0132766; 2004/0147543; and 2004/0176367; and International Patent Application No. PCT/US04/28021 filed on Aug. 27, 2004.

For certain of these embodiments, the IRM compound is an imidazonaphthyridine amine. For certain of these embodiments, the IRM compound is 2-methyl-1-(2-methylpropyl)-1H-imidazo[4,5-c][1,5]naphthyridin-4-amine. For certain of these embodiments, the IRM compound is an imidazoquinoline amine. For certain of these embodiments, the IRM compound is 1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine(imiquimod). For some embodiments, the IRM may have low solubility in water, for example less than about 1 ug/mL (e.g., 0.79 ug/mL in the case of imiquimod), making them difficult to solubilize in aqueous formulations, and potentially using relatively large amounts of oleic acid in the formulation.

The amount of IRM compound that will be therapeutically effective in a specific situation will depend on such things as the activity of the particular compound, the dosing regimen, the application site, the particular formulation and the condition being treated. As such, it is generally not practical to identify specific administration amounts herein; however, those skilled in the art will be able to determine appropriate therapeutically effective amounts based on the guidance provided herein, information available in the art pertaining to IRM compounds, and routine testing. The term “a therapeutically effective amount” means an amount of the IRM compound sufficient to induce a therapeutic or prophylactic effect, such as cytokine induction, inhibition of TH2 immune response, antiviral or antitumor activity, reduction or elimination of postsurgical scarring, reduction or resolution of actinic keratosis or pre-actinic keratosis lesions, reduction in the recurrence of actinic keratosis, treatment of basal cell carcinoma, genital warts, peri-anal warts, molloscum contagiosum, or protection against uv-induced epidermal neoplasia.

In general, the amount of IRM compound present in a topical formulation of the invention will be an amount effective to treat a targeted condition, to prevent recurrence of the condition, or to promote immunity against the condition. In certain embodiments, the amount or concentration of IRM compound is at least 3% by weight, such as, for example, at least 5%, and at least 10%, by weight based on the total weight of the formulation. In other embodiments, the amount of IRM compound is at most 10% by weight, such as, for example, at most 5%, at most 3%, by weight based on the total weight of the formulation. In certain embodiments, the amount or concentration of IRM compound is at least 0.02% by weight, such as, for example, at least 0.03%, at least 0.10%, and at least 0.30% by weight based on the total weight of the formulation.

Fatty Acids

The topical formulations of the invention include fatty acids. In particular, the topical formulations of the invention contain an oleic acid component. As used herein, the term “fatty acid” means a carboxylic acid, either saturated or unsaturated having 6 to 28 carbon atoms, such as, for example, from 10 to 22 carbon atoms.

The fatty acids, including the oleic acid component, may be present in the formulation in an amount sufficient to solubilize the IRM compound. In certain embodiments, the amount of oleic acid component is at least 0.05% by weight, at least 1.0% by weight, at least 3.0% by weight, at least 5.0%, at least 10%, at least 15%, or at least 25%, based on the total weight of the formulation. In certain embodiments, the amount of oleic acid component is at most 40% by weight, at most 30% by weight, at most 15% by weight, or at most 10%, based on the total weight of the formulation.

Compendial grade oleic acid typically contains from 65 to 88 percent (Z)-octadec-9-enoic acid (oleic acid) together with varying amounts of saturated and other unsaturated fatty acids. The composition of fatty acids is determined by gas chromatography using the method described in European Pharmacopeia monograph 01/2005:0799.

For certain embodiments, the oleic acid component contains at least 50%, at least 60%, at least 70% or at least 80% oleic acid. For certain embodiments, the oleic acid component contains at least 80% oleic acid.

For certain embodiments, the oleic acid component is substantially free of polar impurities, such as peroxides. For certain embodiments, the oleic acid component contains less than 10%, less than 5%, less than 1%, or less than 0.1% by weight of polar impurities. For certain embodiments, the oleic acid component has a peroxide value less than 10. For certain embodiments, the oleic acid component has a peroxide value less than 5.

For certain embodiments, the oleic acid component comprises SUPER REFINED Oleic Acid NF, available from Croda Inc., Edison, N.J., USA.

For certain embodiments, the topical formulations of the invention can include fatty acids in addition to those included in the oleic acid component. For example, certain embodiments can include isostearic acid. In some embodiments, the total amount of fatty acids, including those in the oleic acid component, is at least 0.05% by weight, at least 1.0% by weight, at least 3.0% by weight, at least 5.0%, at least 10%, at least 15%, or at least 25%, based on the total weight of the formulation. In certain embodiments, the total amount of fatty acids, including those in the oleic acid component, is at most 40% by weight, at most 30% by weight, at most 15% by weight, or at most 10%, based on the total weight of the formulation.

Antioxidants

For certain embodiments, the topical formulations of the invention can include an antioxidant.

Suitable antioxidants are those that are pharmaceutically acceptable and described in the International Cosmetic Ingredient Dictionary and Handbook, Ninth Edition, Volume 4, 2002, and in the USP NF 2004: The United States Pharmacopeia, 27^(th) Revision and The National Formulary, 22^(nd) Edition.

Examples of suitable antioxidants include ascorbic acid (D and/or L enantiomers), ascorbyl palmitate (D and/or L enantiomers), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), cysteine (D and/or L enantiomers), propyl gallate, sodium formaldehyde sulfoxylate, sodium thiosulfate, and tocopherol.

For certain embodiments, the antioxidant is selected from the group comprising aromatic hydroxy groups capable of hydrogen atom donation. Examples of such antioxidants include BHA, BHT, propyl gallate, and tocopherol.

For certain embodiments, the antioxidant is selected from the group consisting of BHA, BHT, and combinations thereof. For certain embodiments, the antioxidant is BHA.

Preservative System

The formulation often will include a preservative system. The preservative system includes one or more compounds that inhibit microbial growth (e.g., fungal and bacterial growth) within the formulation (for example, during manufacturing and use). The preservative system will generally include at least one preservative compound, such as, for example, methylparaben, ethylparaben, propylparaben, butylparaben, benzyl alcohol, phenoxyethanol, and sorbic acid or derivatives of sorbic acid such as esters and salts. Various combinations of these compounds can be included in the preservative system. In some embodiments of the invention, the preservative system includes methylparaben, propylparaben and benzyl alcohol.

In some embodiments of the invention, the preservative compound is present in an amount of at least 0.01% by weight, such as for example, at least 0.02%, at least 0.03%, at least 0.04%, and at least 0.05%, by weight based on the total weight of the formulation. In other embodiments of the invention the preservative compound is present in an amount of at most 3%, such as for example, at most 2.5%, at most 2.0%, at most 1.0%, at most 0.5%, at most 0.4%, at most 0.3%, and at most 0.2%, by weight based on the total weight of the formulation.

Emollients

The topical formulations of the invention may also include at least one emollient. Examples of useful emollients include but are not limited to long chain alcohols, for example, cetyl alcohol, stearyl alcohol, cetearyl alcohol; fatty acid esters, for example, isopropyl mysristate, isopropyl palmitate, diisopropyl dimer dilinoleate; medium-chain (e.g., 8 to 14 carbon atoms) triglycerides, for example, caprylic/capric triglyceride; cetyl esters; hydrocarbons of 8 or more carbon atoms, for example, light mineral oil, white petrolatum; and waxes, for example, beeswax. Various combinations of such emollients can be used if desired.

In certain embodiments, the amount of the emollient is at least 1.0% by weight, at least 3.0% by weight, at least 5.0% by weight, or at least 10% by weight, based on the total weight of the formulation. In certain embodiments, the amount of emollient is at most 30% by weight, at most 15% by weight, or at most 10% by weight, based on the total weight of the formulation.

Formulations intended for dermal or topical use typically have amounts of an oil phase and an emollient sufficient to provide desirable qualities such as spreadability and feel.

Viscosity Enhancing Agent

The formulations of the present invention can also comprise a viscosity-enhancing agent. Examples of suitable viscosity enhancing agents include long chain alcohols, for example, cetyl alcohol, stearyl alcohol, cetearyl alcohol; cellulose ethers such as hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and carboxymethylcellulose; polysaccharide gums such as xanthan gum; and homopolymers and copolymers of acrylic acid crosslinked with allyl sucrose or allyl pentaerythriol such as those polymers designated as carbomers in the United States Pharmacopoeia. Suitable carbomers include, for example, those available as CARBOPOL 934P, CARBOPOL 971P, CARBOPOL 940, CARBOPOL 974P, CARBOPOL 980, and PEMULEN TR-1 (USP/NF Monograph; Carbomer 1342), all available from Noveon, Cleveland, Ohio.

In certain embodiments, the amount of the viscosity enhancing agent, when used, is at least 0.1% by weight, at least 0.2% by weight, at least 0.5% by weight, at least 0.6% by weight, at least 0.7% by weight, at least 0.9% by weight, or at least 1.0% by weight, based on the total weight of the formulation. In certain embodiments, the amount of the viscosity-enhancing agent, when used, is at most 10% by weight, at most 5.0% by weight, at most 3.0% by weight, at most 2.0% by weight, or at most 1.5% by weight, based on the total weight of the formulation.

Emulsifier

The formulations of the invention can additionally comprise an emulsifier. Suitable emulsifiers include non-ionic surfactants such as, for example, polysorbate 60, sorbitan monostearate, polyglyceryl-4 oleate, polyoxyethylene(4) lauryl ether, etc. In certain embodiments, the emulsifier is chosen from poloxamers (e.g., PLURONIC F68, also known as POLOXAMER 188, a poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), available from BASF, Ludwigshafen, Germany) and sorbitan trioleate (e.g., SPAN 85 available from Uniqema, New Castle, Del.).

If included, the emulsifier is generally present in an amount of 0.1% to 10% by weight of total formulation weight, for example, from 0.5% to 5.0% by weight, and from 0.75% to 4.0% by weight. In certain embodiments, the amount of the emulsifier, if used, is present in an amount of at least 0.1% by weight, at least 0.5% by weight, at least 0.75% by weight, at least 1.0% by weight, at least 2.5% by weight, at least 3.5% by weight, at least 4.0% by weight, or at least 5.0% by weight, based on the total weight of the formulation. In certain embodiments, the amount of the emulsifier, if used, is present in an amount of at most 10% by weight, at most 5.0% by weight, or at most 3.5% by weight, based on the total weight of the formulation.

Some formulations of the invention are oil-in-water emulsions. The water used in these formulations is typically purified water

Optionally, a formulation of the invention can contain additional pharmaceutically acceptable excipients such as humectants, such as for example, glycerin; chelating agents, such as for example, ethylenediaminetetraacetic acid; and pH adjusting agents, such as for example, potassium hydroxide or sodium hydroxide.

In some instances, a single ingredient can perform more than one function in a formulation. For example, cetyl alcohol can serve as both an emollient and a viscosity enhancer.

Illustrative Formulation

In one embodiment of the present invention, a pharmaceutical formulation includes:

5% by weight of 1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine;

28% by weight SUPER REFINED oleic acid;

2.2% by weight cetyl alcohol;

3.1% by weight stearyl alcohol;

3% by weight petrolatum;

3.4% by weight polysorbate 60;

0.6% by weight sorbitan monostearate;

2% by weight glycerin;

0.2% by weight methyl hydroxybenzoate;

0.02% by weight propyl hydroxybenzoate;

0.5% by weight xanthan gum;

2% by weight of benzyl alcohol; and

49.98% by weight water;

wherein the weight percentages are based on the total weight of the formulation.

Methods of Application

Formulations according to the present invention can be applied to any suitable location, for example topically to dermal and/or mucosal surfaces. In the case of dermal application, for example, depending on the IRM compound concentration, formulation composition, and dermal surface, the therapeutic effect of the IRM compound may extend only to the superficial layers of the dermal surface or to tissues below the dermal surface. Thus, another aspect of the present invention is directed to a method for the treatment of a dermal and/or mucosal associated condition comprising applying to skin one of the foregoing formulations. As used herein, a “dermal and/or mucosal associated condition” means an inflammatory, infectious, neoplastic or other condition that involves a dermal and/or mucosal surface or that is in sufficient proximity to a dermal and/or mucosal surface to be affected by a therapeutic agent topically applied to the surface. Examples of a dermal and/or mucosal associated condition include warts, atopic dermatitis, postsurgical scars, lesions caused by a herpes virus, and epidermal neoplasias, such as for example actinic keratosis, pre-actinic keratosis lesions, malignant melanomas, basal cell carcinoma, and squamous cell carcinoma.

In one embodiment, the formulations can be applied to the surface of skin for treatment of actinic keratosis (AK). Actinic keratosis are premalignant lesions considered biologically to be either carcinoma in-situ or squamous intraepidermal neoplasia. AK is the most frequent epidermal tumor and is induced by ultraviolet (UV) radiation, typically from sunlight. Because of its precancerous nature, AK may be considered the most important manifestation of sun-induced skin damage.

In some embodiments, the above-described formulations are particularly advantageous for dermal and/or mucosal application for a period of time sufficient to obtain a desired therapeutic effect without undesired systemic absorption of the IRM compound.

Examples

The following Examples are provided to further describe various formulations and methods according to the invention. The examples, however, are not intended to limit the formulations and methods within the spirit and scope of the invention.

Test Method

A reversed phase high performance liquid chromatography (HPLC) method was used to determine the amount of impurities in cream formulations containing oleic acid.

HPLC parameters: Analytical column: ZORBAX RX C8, 5 micron particle, 15.0×0.46 cm, (available from Agilent Technologies, Wilmington, Del., USA); Detector: UV at 308 nm; Mobile phase: gradient mixture of aqueous ammonium phosphate buffer (prepared by combining 5.1 mL of ortho-phosphoric acid with 985 mL of water and then adjusting to pH 2.5 with concentrated ammonium hydroxide) and acetonitrile; Gradient: start run at 10% acetonitrile, zero initial hold time, then linear gradient to 70% acetonitrile over 15 minutes, zero final hold time; Flow rate: 2.0 mL/minute; Injection volume: 200 μL; Run time: 15 minutes.

Sample solution: A portion (about 300 mg) of the cream formulation was accurately weighed into a volumetric flask (100 mL). Diluent (50 to 60 mL, prepared by combining 250 parts of acetonitrile, 740 parts of water and 10 parts of hydrochloric acid, all parts by volume) was added to the flask. The flask was vortexed until the cream was completely dispersed and then sonicated for a minimum of 5 minutes. The solution was allowed to cool to ambient temperature and then diluted to volume with diluent and mixed. A portion of the solution was filtered using a syringe equipped with a 0.45 micron polypropylene or polytetralfluoroethylene filter to provide the sample solution.

Preparation of Cream Formulations

The cream formulations in Table 1 below were prepared using the following method.

Water phase preparation: A paraben premix was prepared by combining methyl hydroxybenzoate(methylparaben), propyl hydroxybenzoate(propylparaben), and water; heating the mixture with stiffing until the parabens were dissolved; and then allowing the resulting solution to cool to ambient temperature. Glycerin was added to the premix and the mixture was heated to 55±5° C. Xanthan gum was slowly added with mixing. Mixing with heating was continued until the xanthan gum was dispersed.

Oil phase preparation: An imiquimod/oleic acid premix was prepared by combining imiquimod and the oleic acid and then stiffing at ambient temperature overnight. Petrolatum, cetyl alcohol, stearyl alcohol, polysorbate 60, sorbitan monostearate, and butylated hydroxyanisole (BHA), if included, were added to the premix. The oil phase was then heated with stirring to 55±5° C. Benzyl alcohol was added to the oil phase just prior to phase combination.

Phase combination: Both phases were removed from their heat source. The aqueous phase was added to the oil phase and the emulsion was homogenized at high speed for at least 5 minutes. The cream was placed in an ice/water bath while homogenizing and homogenization was continued until the temperature of the cream was 35° C. The homogenizer speed was reduced and homogenization was continued until the temperature of the cream was 25° C.

Table 1 summarizes creams A-D in percentage weight-by-weight basis. The formulations were packaged in glass containers.

TABLE 1 Ingredient A B C D ¹Imiquimod 5 5 5 5 ²Oleic acid, NF 28 28 — — ³SUPER REFINED oleic acid, NF — — 28 28 Cetyl alcohol 2.2 2.2 2.2 2.2 Stearyl alcohol 3.1 3.1 3.1 3.1 Petrolatum 3 3 3 3 Polysorbate 60 3.4 3.4 3.4 3.4 Sorbitan monostearate 0.6 0.6 0.6 0.6 Benzyl alcohol 2 2 2 2 BHA — 1 — 1 Glycerin 2 2 2 2 Methylparaben 0.2 0.2 0.2 0.2 Propylparaben 0.02 0.02 0.02 0.02 Xanthan gum 0.5 0.5 0.5 0.5 Water qs 100 qs 100 qs 100 qs 100 ¹1-(2-methylpropyl)-1H-imidazo[4,5-c]quinolin-4-amine ²J. T. Baker, a division of Mallinckrodt Baker, Inc, Phillipsburg, NJ, USA ³Croda, Inc, Edison, NJ, USA

One set of containers was stored at ambient conditions; the samples used to determine initial values came from these containers. The remaining containers were stored in a constant temperature and humidity chamber at 40° C. at 75% relative humidity. At selected time points, containers were removed from the chamber and then stored at ambient conditions until analyzed. Samples were analyzed using the test method described above for impurities. At the 2, 4, and 6 month time points samples were taken from both the top and the bottom of the containers. The results are shown in Table 2 below where each value is the result of a single determination. Values are not normalized for weight loss that may have occurred during storage.

TABLE 2 Impurities (% wt/wt) Timepoint A B C D ¹Initial - top 0.09 0.08 0.02 0.03 ²2 months - top 0.25 0.32 0.07 0.09 ²2 months - bottom 0.33 0.30 0.04 0.15 ³4 months - top 0.42 0.76 0.18 0.15 ³4 months - bottom 0.46 0.56 0.04 0.29 ⁴6 months - top 0.81 0.30 0.07 0.14 ⁴6 months - bottom 0.49 0.29 0.04 0.07 ¹Creams A, B, C, and D were analyzed 16 days, 15 days, 14 days, and 15 days respectively after they were prepared. ²All samples were analyzed 10 days after the containers were removed from the constant temperature and humidity chamber. ³All samples were analyzed 12 days after the containers were removed from the constant temperature and humidity chamber. ⁴All samples were analyzed 7 days after the containers were removed from the constant temperature and humidity chamber.

The complete disclosures of the patents, patent documents and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated. In case of conflict, the present specification, including definitions, shall control. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. Illustrative embodiments and examples are provided as examples only and are not intended to limit the scope of the present invention. The scope of the invention is limited only by the claims set forth as follows. 

1. A method of preparing a pharmaceutical cream formulated with 1-(2-methylpropyl)-1H imidazo[4,5-c]quinolin-4-amine(imiquimod) and minimizing formation of imiquimod impurities in the prepared pharmaceutical cream during storage of the prepared pharmaceutical cream prior to application of the prepared pharmaceutical cream to a dermal or mucosal surface to treat a dermal or mucosal associated condition, said method comprising: (a) preparing a water phase preparation for formulating the prepared pharmaceutical cream, the water phase preparation comprising pharmaceutically acceptable excipients; (b) preparing an oil phase preparation for formulating the prepared pharmaceutical cream, the oil phase preparation comprising imiquimod and a refined oleic acid component, wherein the refined oleic acid component contains at least about 80% oleic acid by weight as a fatty acid and has a peroxide value of no more than about 5 milliequivalents of oxygen per kilogram and contains less than about 1% by weight polar impurities at or prior to formulation; (c) adding said water phase preparation to said oil phase preparation to form an emulsion; (d) homogenizing the emulsion to formulate the prepared pharmaceutical cream; (e) storing the prepared pharmaceutical cream for at least about six months prior to use of the pharmaceutical cream; and (f) minimizing the formation of imiquimod impurities in the pharmaceutical cream during said storing of the pharmaceutical cream, as compared to an amount of imiquimod impurities formed in an identical pharmaceutical imiquimod cream but formulated with a compendial grade oleic acid component rather than the refined oleic acid component when the pharmaceutical cream and the identical pharmaceutical imiquimod cream are each stored under identical storage conditions, so that the formation of imiquimod impurities in the pharmaceutical cream is minimized and a therapeutically effective amount of imiquimod can be delivered from the pharmaceutical cream to treat the dermal or mucosal associated condition when the pharmaceutical cream is applied to a dermal or mucosal surface following said storing of the pharmaceutical cream.
 2. The method of claim 1, wherein said pharmaceutical cream contains imiquimod impurities in an amount of no more than about 0.14% wt./wt. after storage of said pharmaceutical cream for about two months, where absorbance of said pharmaceutical cream is analyzed at about 308 nm using a UV detector.
 3. The method of claim 1, wherein said pharmaceutical cream contains imiquimod impurities in an amount of no more than about 0.07% wt./wt. after storage of said pharmaceutical cream for about two months, where absorbance of said pharmaceutical cream is analyzed at about 308 nm using a UV detector.
 4. The method of claim 1, wherein said pharmaceutical cream contains imiquimod impurities in an amount of no more than about 0.04% wt./wt. after storage of said pharmaceutical cream for about two months, where absorbance of said pharmaceutical cream is analyzed at about 308 nm using a UV detector.
 5. The method of claim 1, wherein said pharmaceutical cream further comprises an antioxidant selected from the group consisting of butylated hydroxyl toluene (BHT) and butylated hydroxyanisole (BHA).
 6. The method of claim 1, wherein the imiquimod is present in an amount of not more than 10% by weight based on the total weight of said pharmaceutical cream and wherein the oleic acid component is present in an amount of no more than about 40% by weight based on the total weight of said pharmaceutical cream.
 7. The method of claim 1, wherein the imiquimod is present in an amount of about 5% by weight based on the total weight of said pharmaceutical cream and wherein the oleic acid component is present in an amount of about 28% by weight based on the total weight of said pharmaceutical cream.
 8. A method of claim 7, said method including the further step of: forming a premix comprised of imiquimod and the oleic acid component before said preparing of the oil phase preparation.
 9. A method of claim 7, said method including the further step of: adding petrolatum, certyl alcohol, stearyl alcohol, polysorbate, sorbitan monostearate to the premix.
 10. A method of claim 7, said method including the further step of: adding BHA to the premix.
 11. A method of claim 8, said method including the further steps of: stiffing the premix; and heating the premix while said stirring to about 55° C.
 12. A method of claim 9, said method including the further steps of: stirring the premix; and heating the premix while said stirring to about 55° C.
 13. A method of claim 8, said method including the further step of: adding benzyl alcohol to the oil phase preparation.
 14. A method of claim 9, said method including the further step of: adding benzyl alcohol to the oil phase preparation.
 15. A method of claim 10, said method including the further step of: adding benzyl alcohol to the oil phase preparation.
 16. A method of claim 11, said method including the further step of: adding benzyl alcohol to the oil phase preparation.
 17. A method of claim 1, wherein said homogenizing was for about 5 minutes at high speed.
 18. A method of claim 1, said method including the further steps of: forming a paraben premix comprised of methyl hydroxybenzoate, propyl hydroxybenzoate and water before said preparing of the water phase preparation; stiffing and heating the paraben premix until the methyl hydroxybenzoate and propyl hydroxybenzoate are dissolved in the water; and cooling the heated and stirred paraben premix in which the methyl hydroxybenzoate and propyl hydroxybenzoate are dissolved.
 19. A method of claim 15, said method including the further steps of: adding glycerin to the cooled paraben premix; and heating the cooled paraben premix mixed with glycerin to a temperature of about 55° C.
 20. A method of claim 16, said method including the further steps of: adding xanthan gum to the heated paraben premix mixed with glycerin; and mixing and heating the heated paraben premix mixed with glycerin and xanthan gum until the xanthan gum is dispersed in the heated paraben premix mixed with glycerin and xanthan gum. 